The Browns won a divisional title one year with a record of 8-8 and in 1994 at the time the labor impasse stopped games the Rangers were in 1st place in the Western Division despite being 10 games under .500.

Had they played the rest of the final six weeks it's very doubtful Texas could have won enough to finish over .500 (all the other teams were even worse in the standings...) So it probably would have happened in baseball for the first time.

Lip

If you are talking about the NFL, it was 1985.

More recently, the Chargers in 2008 and Denver in 2011 both won divisions at 8-8. Seatle won their division at 7-9 in 2010. All three of those teams ended up winning a playoff game.